1. Field of the Invention
The invention relates to diagnostic systems and, more particularly, to a diagnostic system for a valve that can be actuated by a position controller via a drive.
2. Description of the Related Art
In many areas of process control engineering and power engineering, trouble-free operation of an installation depends on the proper functioning of the shut-down and control valves that are used. In order to avoid cost-intensive, irregular operational interruptions, it should be possible to detect valve damage as far as possible already in the initial stage, i.e., before a failure of a valve can cause stoppage of the installation. For example, defective valve seats lead to leakage flows that produce a broadband sound emission. Recording and evaluation of the sound emission of a valve can therefore serve to provide earlier detection of valve damage. Since valve damage can lead to faults and expensive consequential cost, it is very useful to conduct a diagnosis, possibly with automatic acquisition and programmable evaluation of the faults. Statistical evaluations of diagnostic data can serve the purpose both of optimizing the servicing processes to replace a damaged valve in good time, and also of assessing the quality of valve manufacturers and classifying them, or of assessing the suitability of specific valves for various types of processes.
DE 199 24 377 A1 discloses a diagnostic system for a valve that can be actuated by a position controller via a drive and has a device for acquiring, storing and evaluating structure-borne noise spectra measured at the valve. In order to enable a particularly reliable valve diagnosis, it is possible to store in the device for acquisition, storage and evaluation a structure-borne noise spectrum acquired with an intact valve that is slightly open.
For the purpose of diagnosis, a structure-borne noise spectrum acquired with a closed valve is compared with what has been stored, and the similarity is used as a criterion for the leakage of the valve. The known diagnostic system has the disadvantage, however, that the acquisition, storage and evaluation of structure-borne noise spectra for the purpose of establishing a leak flow is comparatively expensive. Particularly in the case of Emergency Shut-Down (ESD) valves, however, the desire is to have a simple diagnostic system that can be used by the operator of an installation to establish whether these valves are leaking.